1. Field of the Invention
The present invention relates to processes and apparatus for the removal of mercury contaminants from waste materials. In particular, the present invention describes a thermal recovery process (which allows ambient air to be present within the system) and apparatus for the efficient removal of mercury and the recovery of mercury from waste materials, especially waste materials such as batteries, crushed lamps, switches and the like.
2. Background of the Art
One of the many serious forms of pollution which has been created by industry has been the levels of mercury introduced into the environment from manufactured goods. Amongst the more prominent incidents involving mercury were the Minnimata contamination in Japan and the swordfish warnings in the 1950""s. At Minnimata, mercury waste from a local manufacturing company contaminated a bay and many local residents ingested high levels of mercury from fish. The effects of mercury, like those of many heavy metals, are quite devastating, prolonged, and difficult to treat. Mercury is particularly dangerous because, even though it is a liquid and its boiling point is about 675xc2x0 F. (356.6xc2x0 C.), it is hygroscopic or hydroscopic and enters the surrounding air and water system quickly. It is also injurious in small doses which can be rapidly ingested from breathing contaminated air and is highly persistent after it has been ingested.
Even with its serious potential for harm, mercury has many significant commercial uses and is widely accepted in the electrical and electronics area as a conductor. Mercury is conventionally used, for example, as a component in batteries, as a contact for electrical switches, as circuit connectors and switches in thermostats, and as conductors in fluorescent lamps. Because of the large volume of use for mercury, there is also a large volume of mercury waste which is created each year. Mercury may not be deposited in solid waste landfills because of its known hazardous effects on the environment, and burying it is merely a temporary and unsafe disposal method since mercury will readily enter the water table and spread in the environment. It can be further distributed within the ecosystem if ingested by bacteria, insects or the like.
One method of recovering mercury commercially is to take the waste products containing mercury, place them within a drum or container (e.g., a fifty-five gallon drum), place the container within an autoclave, and heat the container well above the boiling point of mercury to evaporate the mercury into a collection point (e.g., condensation chamber).
Earlier, non-public attempts by the present inventors at such mercury collection systems used long, repeating cooling pipes (much like steam radiators) to air cool the mercury in the heated waste stream from the autoclave. Solidified (liquefied) mercury would be drained from the pipe (with other condensed materials) and the residue of the waste stream would then be cooled to further condense materials (including additional mercury) in the waste stream. This process would have been highly inefficient, and would have been quite costly to run. The long length of cooling pipes needed for the process would clog from deposited mercury (usually in the form of amalgams or cocondensed waste) within the pipes, the lining of the pipes could easily react with the mercury, causing removal and/or deposition of metal or amalgam, extreme amounts of heat would be produced locally around the pipes which would require cooling measures for the work environment, and other adverse features of this attempted arrangement dictated against this type of process. The volume capability of systems which work only with batch processing of waste containing mercury also greatly limit the ability of such systems to address the volume requirements of mercury waste treatment needs.
To respond to the need for more efficient and improved quality recovery and removal of mercury from water streams, improved processes and equipment are needed.
The present invention relates to a process and apparatus for the removal of mercury from waste materials and for the recovery of mercury in an environmentally safe and economic manner. The method is performed by apparatus which heats the mercury waste (in a batch or continuous fashion) and which recovers mercury from the effluent vapor stream from the heating step by repeated, controlled cooling of the vapor stream to selectively condense materials from the vapor stream. The heated vapor stream is first cooled from the high temperatures directly emitted from a heating zone (at temperatures above 1000xc2x0 F. [538xc2x0 C.]) down to a temperature above the boiling point of mercury (xcx9c675xc2x0 F. [xcx9c357xc2x0 C.]) to remove additional pollutants from the stream other than the major portion of the mercury. This is followed by subsequent cooling of the vapor stream to a temperature below the boiling point of mercury, and then preferably transferred to a third cooling zone which further condenses the majority of condensable residues in the heated vapor stream. The gaseous stream may then be further filtered to reduce the amount of other hazardous pollutants in the vapor (gas) stream. This is preferably done by a system of scrubbers and filters. By this process and the described apparatus, very high percentages of the mercury in the waste can be recovered with little or no introduction of mercury into the waste stream or the environment.